the rite answer i guess shud be b)....

there is an expression for the sum of all factors of p₁^ap₂^bp₃^c........where p1, p2 , p3 are prime numbers....

which is (p₁^a+1-1)/(p₁-1) * (p₂^b+1-1)/(p₂-1)*...........

so applying this u get the above result..........

rate if useful........